61 lines
2.4 KiB
C++
61 lines
2.4 KiB
C++
/*
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* Copyright (C) 2019-2020 The DOSBox Team
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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#ifndef DOSBOX_COMPILER_H
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#define DOSBOX_COMPILER_H
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// This header wraps compiler-specific features, so they won't need to
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// be hacked into the buildsystem.
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// Modern C++ compilers have better support for feature testing using GNU
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// extension __has_attribute but C++20 introduces even better alternative:
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// standard-defined __has_cpp_attribute, which will remove the need for
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// defining C_HAS_* macros on a buildsystem level (at some point).
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// The __attribute__ syntax is supported by GCC, Clang, and IBM compilers.
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//
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// TODO: C++11 introduced standard syntax for implementation-defined attributes,
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// it should allow for removal of C_HAS_ATTRIBUTE from the buildsystem.
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// However, the vast majority of GCC_ATTRIBUTEs in DOSBox code need
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// to be reviewed, as many of them seem to be incorrectly/unnecessarily
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// used.
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#if C_HAS_ATTRIBUTE
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#define GCC_ATTRIBUTE(x) __attribute__ ((x))
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#else
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#define GCC_ATTRIBUTE(x) /* attribute not supported */
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#endif
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// GCC_LIKELY macro is incorrectly named, because other compilers support
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// this feature as well (e.g. Clang, Intel); leave it be for now, at
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// least until full support for C++20 [[likely]] attribute will start arriving
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// in new compilers.
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//
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// Note: '!!' trick is used, to convert non-boolean values to 1 or 0
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// to prevent accidental incorrect usage (e.g. when user wraps macro
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// around a pointer or an integer, expecting usual C semantics).
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#if C_HAS_BUILTIN_EXPECT
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#define GCC_LIKELY(x) __builtin_expect(!!(x), 1)
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#define GCC_UNLIKELY(x) __builtin_expect(!!(x), 0)
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#else
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#define GCC_LIKELY
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#define GCC_UNLIKELY
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#endif
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#endif /* DOSBOX_COMPILER_H */
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